1. Technical Field
The present invention relates to a high-frequency power amplifying apparatus including a plurality of series-connected amplifiers, and more particularly, to a high-frequency power amplifying apparatus for delivering, with a reduced loss, the output of that one of the series-connected amplifiers which is selected in accordance with the demanded output power, thereby attaining a high power efficiency.
2. Related Art
The transmission output of a cellular phone is not required to be always maintained at its maximum level, and may be decreased if the distance between the cellular phone and a base station for the other end of the phone line is short. In general circumstances, the cellular phone is operable with stability at a transmission output level which is one-tenth of the maximum level. By decreasing the transmission output in this manner, waste power consumption can be prevented and the best possible use of capacity of a power source secondary battery of the cellular phone can be achieved, to thereby permit the cellular phone to operate for a long time.
To variably control the output of a high-frequency power amplifying apparatus comprised of series-connected amplifiers, one of these amplifiers is selected in accordance with the demanded output power, and the output of the selected amplifier is supplied to the output terminal of the power amplifying apparatus, as described in Japanese provisional patent publication no. 4-260209. Thus, a high-frequency input signal to the power amplifying apparatus is amplified by one or more amplifiers arranged on the upstream side (i.e., pre-stage side) of the selected amplifier and then amplified by the selected amplifier. The resultant amplified signal is delivered from the power amplifying apparatus, bypassing one or more amplifiers arranged on the downstream side (i.e., post-stage side) of the selected amplifier. When the first-stage amplifier is selected so that there is no upstream amplifier for the selected amplifier, the input signal amplified by the first-stage amplifier is delivered from the power amplifying apparatus, bypassing the second- to final-stage amplifiers. When the final-stage amplifier is selected so that there is no downstream amplifier for the selected amplifier, the input signal amplified by the first- to final-stage amplifiers is delivered from the power amplifying apparatus.
As shown by way of example in FIG. 4, the high-frequency power amplifying apparatus of this type is comprised of first- and second-stage amplifiers 1 and 2 connected in series with each other, and a switch circuit 3 controlled by a control circuit 5. The switch circuit 3 is arranged between the output terminal of the first-stage amplifier 1, the input terminal of the second-stage amplifier, and a bypass circuit that is provided with a half-wavelength delay line (xcexg/2 line) 4 and connected to the output terminal 6b of the power amplifying apparatus. Reference numeral 6a denotes the input terminal of the power amplifying apparatus; 7a, a matching circuit disposed between the first-stage amplifier 1 and the switch circuit 3; and 7b, a matching circuit disposed between the second-stage amplifier 2 and the output terminal 6b. 
When a high output power is demanded, the switch circuit 3 is switched to the second-stage amplifier 2, so that the output of the first-stage amplifier 1 may be amplified by the second-stage amplifier 2 to obtain a high output. When a low output power is requested, the switch circuit 3 is switched to the bypass circuit, so that the output of the first-stage amplifier 1 may be delivered as a low output from the power amplifying apparatus, bypassing the second-stage amplifier 2.
With this power amplifying apparatus, a high output can be taken from the second-stage amplifier 2 without problems, because a resistance for input signal at the bypass-circuit contact 3a becomes large when the switch circuit 3 is connected to the second-stage amplifier 2 to open the contact 3a and because the half-wavelength delay line 4 is provided in the bypass circuit.
When the switch circuit 3 is connected to the bypass circuit to obtain a low output power, however, the output impedance of the second-stage amplifier 2, as viewed from the output terminal 6b, has a value which is not negligible with respect to a load (not shown) such as an antenna since the second-stage amplifier 2 is connected to the output terminal 6b of the power amplifying apparatus. For this reason, when the switch circuit 3 is connected to the bypass circuit, the second-stage amplifier 2 serves as a load for the first-stage amplifier 1, causing an increased loss.
Another type of high-frequency power amplifying apparatus is disclosed in Japanese provisional patent publication no. 2000-165164. As shown in FIG. 5, this power amplifying apparatus comprises a directional coupler 8 for receiving outputs of first- and second-stage amplifiers 1 and 2 and a terminal switch 9 controlled by a control circuit 5, so that the isolation terminal 8a of the directional coupler 8 may be terminated with a predetermined impedance 9a or may be opened or short-circuited by means of the terminal switch 9, thereby varying the terminal impedance of the directional coupler 8.
With this power amplifying apparatus, a loss in the directional coupler 5 can be decreased to some extent by causing the isolation terminal 8a of the directional coupler 8 to be opened or short-circuited when the switch circuit 3 is connected to the second-stage amplifier 2 to obtain a high output.
However, such an arrangement entails upsizing of the power amplifying apparatus since it includes the directional coupler 8, and entails an increased loss especially when it delivers a low output since the directional coupler 8 is provided through which the output of each amplifier 1 or 2 is supplied to the output terminal 6b. 
An object of the present invention is to provide a high-frequency power amplifying apparatus which is simple in construction and which is capable of generating a variable output at a high power efficiency by supplying the output of the desired one of a plurality of series-connected amplifiers, with a reduced loss, to the output terminal of the amplifying apparatus.
A high-frequency power amplifying apparatus according to the present invention comprises: a plurality of amplifiers including at least first- and final-stage amplifiers and connected in series with one another in increasing order of saturation power; an input terminal connected to the first-stage amplifier; an output terminal connected to the final-stage amplifier; a power controller for selectively supplying the output terminal with an output from a desired one of the plurality of amplifiers in accordance with an externally demanded output power and for causing one or more amplifiers downstream of the desired one amplifier to be in a cutoff state when the desired one amplifier is not the final-stage amplifier; and an output delay line connected between the output terminal and the final-stage amplifier and having a line length thereof providing the final-stage amplifier with a high impedance as viewed from the output terminal when the final-stage amplifier is in a cutoff state.
According to the present invention, it is unnecessary to provide a directional coupler between the plurality of amplifiers and the output terminal of the power amplifying apparatus, and accordingly a loss is eliminated which is caused by the directional coupler. Thus, the power efficiency of the power amplifying apparatus can be improved and the power amplifying apparatus can be simplified in construction. In addition, when the output of an arbitrary amplifier disposed upstream of the final-stage amplifier is selectively supplied to the output terminal of the apparatus, the high-impedance output delay line prevents one or more amplifiers, if any, disposed downstream of the arbitrary amplifier from constituting a substantial load for the first-stage amplifier through the arbitrary amplifier. This makes it possible to supply the output of the arbitrary amplifier to the output terminal of the power amplifying apparatus without causing a substantial loss, bypassing the one or more downstream amplifiers, thereby permitting the power amplifying apparatus to deliver a variable output at a high power efficiency. In particular, the power efficiency at the time of delivering a low or medium power output can be improved.
In the present invention, preferably, the power amplifying apparatus further comprises one or more switch circuits each interposed between the output terminal of the power amplifying apparatus and corresponding two adjacent amplifiers among the plurality of amplifiers. The power controller closes a desired one of the one or more switch circuits in accordance with the demanded output power.
With this preferred arrangement, by closing a desired one switch circuit, the output of a desired one amplifier can be selectively supplied to the output terminal of the power amplifying apparatus.
Preferably, the power amplifying apparatus further comprises one or more bias switches individually interposed between bias voltage sources and the plurality of amplifiers other than the first-stage amplifier. The power controller opens at least one bias switch corresponding to one or more amplifiers disposed downstream of the desired one amplifier when the desired one amplifier is not the final-stage amplifier.
With this preferred arrangement, a cutoff state can be attained for one or more amplifiers downstream of a desired one amplifier by opening at least one bias switch.
Preferably, the line length of the output delay line is set to a length that provides the final-stage amplifier with a high pure resistance as viewed from the output terminal of the power amplifying apparatus when the final-stage amplifier is in a cutoff state.
According to this preferred arrangement, when the output of the arbitrary amplifier is supplied to the output terminal of the power amplifying apparatus, one or more amplifiers downstream of the arbitrary amplifier can be positively prevented from constituting a load for the first-stage amplifier through the arbitrary amplifier, whereby the power efficiency can be improved.
Preferably, each of the one or more switch circuits has a first on-off contact whose one side is connected between two amplifiers associated therewith, a second on-off contact interposed between another side of the first on-off contact and the output terminal of the power amplifying apparatus, and a third on-off contact whose one side is connected between the first and second on-off contacts and another side thereof is grounded. Under the control of the power controller, the third on-off contact is closed when the first and second on-off contacts are open and is opened when the first and second on-off contacts are closed.
With this preferred arrangement, when the first and second on-off contacts are open, the degree of isolation therebetween can be made sufficiently high enough to prevent leakage of a high-frequency signal through the first and second contacts between each amplifier and the terminal output of the amplifying apparatus, thereby reducing a loss and making each switch circuit compact in size.
Preferably, the power amplifying apparatus further comprises a plurality of output matching circuits that are connected individually to output sides of the plurality of amplifiers and serve to increase output impedances of the plurality of amplifiers. More preferably, each output matching circuit increases the output impedance of a corresponding one amplifier in the order of approximately 200 ohms.
With this preferred arrangement, it is possible to reduce a loss caused by an on-resistance observed when a switch circuit corresponding to a desired one of the plurality of amplifiers is closed so as to supply the output of the desired one amplifier to the output terminal of the power amplifying apparatus.
Preferably, the power amplifying apparatus further comprises an impedance conversion circuit connected between the one or more switch circuits, the output delay line and the output terminal of the power amplifying apparatus and serves to match the output from each of the plurality of amplifiers to an output-terminal impedance of the power amplifying apparatus. For instance, the output-terminal impedance of the power amplifying apparatus is set at 50 ohms.
With the preferred arrangement, the power amplifying apparatus is enabled to supply its output power to a load such as an antenna with a reduced loss and at a high power efficiency.
Preferably, the power amplifying apparatus further comprises one or more first bypass delay lines each of which is xc2xc wavelength long and is interposed between a corresponding one of the plurality of amplifiers and the switch circuit associated therewith.
In this preferred arrangement, bypass circuits are formed, which individually permit outputs of one or more amplifiers other than the final-stage amplifier to be supplied to the output terminal of the power amplifying apparatus. When the output of an arbitrary one amplifier is supplied to the output terminal, the switch circuit of at least one bypass circuit corresponding to the remaining one or more amplifiers is opened to disconnect the at least one bypass circuit from the amplifier associated therewith. Since each bypass circuit is provided with the first bypass delay line, the bypass circuit disconnected from the amplifier associated therewith has high impedance, so that a loss in the bypass circuit may be reduced. The influence of the on-resistance of each switch circuit, observed when the switch circuit is closed, onto the supply of the amplifier output to the output terminal of the power amplifying apparatus can be reduced, so that each switch circuit entails a reduced loss.
More preferably, each of the one or more switch circuits has a first on-off contact interposed between the amplifier associated therewith and the output terminal of the power amplifying apparatus, a second on-off contact interposed between the associated amplifier and a grounding. Under the control of the power controller, the second on-off contact is closed when the first on-off contact is open and is opened when the first on-off contact is closed.
With this preferred arrangement, the degree of isolation between the amplifier and the output terminal of the power amplifying apparatus observed when the first on-off contact is open is increased, so that a loss caused by leakage of a high-frequency signal between the amplifier and the output terminal may be decreased.
Preferably, the power amplifying apparatus provided with one or more first bypass delay lines each of which is xc2xc wavelength long, further comprises a second bypass delay line which is interposed between the output terminal of the power amplifying apparatus and the one or more switch circuits and which is xc2xc wavelength long.
In this preferred arrangement, each of bypass circuits for permitting amplifier outputs to be supplied to the output terminal of the power amplifying apparatus includes the first and second bypass delay lines. With this arrangement, when each bypass circuit is disconnected from the amplifier associated therewith, the impedance of the bypass circuit as viewed from the amplifier and the impedance of the bypass circuit as viewed from the output terminal of the power amplifying apparatus have sufficiently increased values. This makes it possible to suppress the influence of each bypass circuit onto the transmission of a high-frequency signal from the amplifier immediately upstream of the bypass circuit to the amplifier immediately downstream thereof and onto the signal output from the final-stage amplifier. Thus, a high-frequency signal can be amplified by the first- to final-stage amplifiers with a reduced loss and can be taken from the final-stage amplifier. When the output from a desired one amplifier is supplied through the associated bypass circuit to the output terminal of the power amplifying apparatus, the first and second bypass delay lines of the bypass circuit constitute, as a whole, a delay line which is xc2xd wavelength long, so that the amplifier output may be supplied to the output terminal of the power amplifying apparatus with a reduced loss.
Preferably, each switch circuit has a first on-off contact interposed between the first and second bypass delay lines, a second on-off contact interposed between a grounding and a connection between the first bypass delay line and the first on-off contact, and a third on-off contact interposed between a grounding and a connection between the first on-off contact and the second bypass delay line. Under the control of the power controller, the second and third on-off contacts are closed when the first on-off contact is open and are opened when the first on-off contact is closed.
With this preferred arrangement, when the first on-off contact of each switch circuit is opened, the first bypass delay line has a sufficiently high impedance as viewed from the amplifier corresponding to the switch circuit and the second bypass delay line has a sufficiently high impedance as viewed from the output terminal of the power amplifying apparatus. Thus, the bypass circuit disconnected from the associated amplifier can have a high impedance, whereby a loss attributable to the bypass circuit can be decreased.
Preferably, the power amplifying apparatus further comprises a plurality of input matching circuits each connected to an input side of a corresponding one of the plurality of amplifiers. Each input matching circuit performs impedance-matching of a high-frequency signal, supplied from the input terminal of the power amplifying apparatus or the amplifier immediately upstream of the input matching circuit, to the amplifier immediately downstream of the input matching circuit.
With this preferred arrangement, a high-frequency signal can be transmitted between adjacent two amplifiers with a reduced loss.
More preferably, the power amplifying apparatus further comprises a plurality of input delay lines. Each input delay line is interposed between the input matching circuit associated therewith and the amplifier immediately upstream of the input matching circuit, and serves to increase the impedance of a downstream amplifier as viewed from an upstream amplifier when the switch circuit is open, which is connected at its one side between the upstream amplifier and the downstream amplifier. The upstream amplifier is disposed immediately upstream of the input delay line, and the downstream amplifier is disposed immediately downstream of the upstream amplifier.
According to this preferred arrangement, when a switch circuit is open and the amplifier downstream of the switch circuit is in a cutoff state, the interference between the amplifiers disposed upstream and downstream of the switch circuit can be effectively prevented.
The power amplifying apparatus provided with the plurality of amplifiers constituted by the first- and final-stage amplifiers may comprise a circulator interposed between the output delay line and the output terminal of the power amplifying apparatus. The circulator has a first terminal for receiving an output of the first-stage amplifier through the switch circuit associated therewith, a second terminal for receiving an output of the final-stage amplifier through the output delay line, and a third terminal connected to the output terminal of the power amplifying apparatus, and is configured to transmit a signal received at the first terminal to the second terminal and then transmit the same to the third terminal, and transmit a signal received at the second terminal to the third terminal, thereby supplying the output from the first-stage or final-stage amplifier to the output terminal of the power amplifying apparatus.
With this preferred arrangement, the output of the final-stage amplifier can be supplied through the second and third terminals of the circulator to the output terminal of the power amplifying apparatus with a reduced loss without causing leakage of the output of the final-stage amplifier to the first-stage amplifier. Since the output delay line is interposed between the circulator and the final-stage amplifier and hence the final-stage amplifier has a sufficiently high impedance as viewed from the output terminal of the power amplifying apparatus, the output from the first-stage amplifier can be supplied to the output terminal of the power amplifying apparatus with a reduced loss.